docs: def on_delete_record(event):
      """When a resource record is deleted, delete all related attachments.
      When a bucket or collection is deleted, it removes the attachments of
      every underlying records.
      """
      keep_old_files = asbool(utils.setting_value(event.request, 'keep_old_files', default=False))
      if keep_old_files:
          return
  
      # Retrieve attachments for these records using links.
      resource_name = event.payload['resource_name']
      filter_field = '%s_uri' % resource_name
      uri = event.payload['uri']
      utils.delete_attachment(event.request, link_field=filter_field, uri=uri)